/in/foo.cc: In function 'int main()':
/in/foo.cc:11:17: warning: 'ch' may be used uninitialized in this function [-Wmaybe-uninitialized]
     while(ch<'0'||ch>'9'){ch=getchar();if(ch=='-') f=-1;}
           ~~~~~~^~~~~~~~
/in/foo.cc:10:19: note: 'ch' was declared here
     int res=0,f=1,ch;
                   ^~